Production of rubber articles



Patented F eb. 20, 1934 UNIT STATES PATENT ()FFICE PRODUCTION OF RUBBER ARTICLES a British company No Drawing. Application March 16, 1933, Serial No. 661,086, and in 1932 6 Claims.

This invention is concerned with improve-- ments in the production of articles of, or containing, rubber and is particularly concerned with a process for the production of threads,

filaments or tubes from aqueous dispersions of organic materials of the kinds hereinafter specified. V

In Patent No. 1,887,190, a process is described and claimed for the manufacture of filaments, threads and tubes of rubber or the like material from aqueous dispersions of the kinds specified therein by causing the dispersions to flow through orifices or jets of any desired shape into contact with a liquid dehydrating and setting medium operating partly or entirely under continuous penetrative osmotic action.

According to the prior process the liquid dehydrating and setting medium is preferably a Warm concentrated solution of a saline or other very soluble substance of the type described in British Patent No. 303,544 as, for instance, the concentrated solutions of alkali metal and ammonium salts such as sodium chloride, ammonium chloride or ammonium acetate, or mixtures of such salts, and with or without an acid such as acetic acid or mixture. of acids.

Working with dehydrating and setting liquids substantially neutral, it is usually desirable for the production of coarse counts to use the dehydrating and setting liquid at 80 to 85 C. and, for the production of threads of line counts, to use the aforesaid liquids at above about 40 C. It is, however, desirable to be able to work at as low a temperature as possible. 35 Although the mere addition of acidto the dehydrating and setting liquids would permit working at a lower temperature, it has been'found nevertheless to be desirable, particularly when causing aqueous dispersions of rubber or the like to flow through orifices or jets under no substantial pressure or head, to use a dehydrating and setting salt solution which has only sufiicient setting effect on the surface of the latex stream immediately it leaves the orifice or jet to retain the shape of the latter, and which only causes the formation of a loose permeable type of coagulum.

It has been proposed, for instance, to produce non-fibrous thread by extruding latex directly into a coagulating bath of acetic acid with or without zinc acetate, or into a coagulating bath or alcohol alone, but such coagulants exert an immediate, strong coagulating effect on the latex stream immediately it imerges from the orifice. Although this procedure is, in general, satisfac- Great Britain April 19,

tory it is not so satisfactory in the production of thread of coarse counts. With threads having a diameter for instance, of over 1/2() inch there is a considerable tendency for the tough skin of coagulum which may be formed around the issuing latex stream to impede the setting at the centre of the thread. This may necessitate longer treatment in the coagulant solution before the thread may be safely handled without fear of blistering as when dried by heat, or of distortion due to mechanical handling. On the other hand, a weak, gentle type of coagulant does not give rise to a strong skin.

The object of the present invention is to modify the process described and claimed in Patent No. 1,887,190 so as to accelerate the rate of formation of thread and so as to permit the process being run continuously for a long time without serious attention, 7 According to the present invention the process for the manufacture of threads, filaments and tubes of or containing rubber or the like materials from aqueous dispersions of the kinds hereinafter specified, wherein the aqueous dispersions are caused to flow through orifices or jets of any desired shape into contact with a liquid dehydrating and setting medium operating partly or entirely under continuous penetrative osmotic action, comprises employing as the liquid dehydrating and setting medium a mixture comprising a concentrated solution of a largely'dissociated salt of a weak acid that is capable of being largely dissociated and hydrolyzed, and the weak acid itself, preferably added in such amount that the pH value of the medium is not lower than 5.0 and so conditioning the aqueous dispersions to be employed as to make them set readily when brought into contact with the aforesaid weakly acidic dehydrating and setting medium by adding substances that are substantially inactive to the dispersions aforesaid, but capable of being decomposed when brought into contact with the aforesaid weakly acidic medium into substances inducing coagulation within'the aqueous dispersions aforesaid.

The liquid dehydrating and setting media used according to the present invention are buffer solutions.

It is well known (see for instance Washburn, J. Amer. Chem. Soc., 1908, 30, 36) that it is pos- 105 sible to obtain acid solutions which, although they contain only a small concentration of hydrogen ions are, nevertheless, capable of neutralizing reatively large amounts of alkali. Such solutions usually consist of a weak acid in the pres- 110 ence of its largely dissociated salt. These solu- V tions which are able to resist to a subtantial solutions.

'ing and setting solutions, are the ammonium and 'ethanolamine soaps of the fatty acids and colophony. In general the substances which can be employed in this connection consist of a weak acid and a weak base and which are readily decomposed by even a weakly acid coagulant.

By admixing substances of this nature with the aforesaid dispersions, a coagulant is developed in situ in the dispersions by their interaction with the dehydrating and setting solution, thereby enhancing the rate of coagulation at the centre of the thread.

Working according to the present invention, it is found that the rate of extrusion for a given head is increased, that the absence of rapid setting at the orifices or jets lessens the risk of partial or complete blockage of the apertures, and also that a wider range of thread sizes can be obtainedfrom any particular orifice by varying the level of the orifice below that of the surface of the coagulant solution than can be obtained by employing a more active coagulant.

A further advantage obtained in the use of a coagulant of pH value greater than 5.0 is that the risk of porosity in the thread due to decomposition of substances decomposable by acids with evolution of gases, such as sulphides and carbonates, is greatly reduced.

The dispersions comprise those consisting of or containing rubber, gutta-percha, balata or similar vegetable resins occurring naturally, or artificially obtained.

Such artificial aqueous dispersions may include those of coagulated rubber, vulcanized rubber,

synthetic rubber, waste or reclaim. If desired, any of the aforementioned dispersions may be used alone or in admixture with one another.

Any of the aforesaid dispersions may contain the usual known compounding ingredients and/ or may be in concentrated form.

Concentrates such as are obtained in Patent 1,846,164, February 23, 1932, to which may be added any one or more or the usual compounding ingredients, may also be used.

It has been experimentally ascertained that if for example, ammonium oleate as such is added to a concentrated solution of ammonium acetate and acetic acid wherein the acetic acid is added in such amount that the pH value of the medium is not lower than 5.0, free oleic acid is produced as can be seen by the oily drops of oleic acid which rise to the surface.

It has also been shown that if oleic acid is added as an aqueous dispersion to blown rubber latex containing very small amounts, or no ammonia, coagulation of the rubber latex takes place within twenty four hours.

Moreover, it has been experimentally shown that the type of dehydrating and setting bath described herein is by itself 7 insufficient to produce satisfactory coagulation of the latex, particularly at normal temperatures. Such a bath may cause inappreciable coagulation, or may produce a weak type of coagulum incapable of remaining in continuous thread formation, or of being conveyed out of the setting bath.

On the other hand, the addition of, for instance, ammonium oleate to the latex leads to an enhanced coagulation when the thus treated rubber latex is contacted with the dehydrating and setting bath. It is considered, therefore, that some reaction must occur within the rubber thread which is being produced. This reaction within the thread is considered to be the decomposition or", for instance, ammonium oleate by the slightly acidified dehydrating and setting bath to produce free oleic acid in situ in the thread in sufficient proportion to cause coagulation in the interior of the thread.

Experimental work has shown that this effect is not dependent on the presence of a second substance in the thread such. as zinc oxide which might be capable of producing coagulating ions by reaction with the substantially inactive substances.

The following examples illustrate how the process can be eliected for the production of thread of 30s and 20s count:-

Example 1 For the production of thread having a diameter .i the order of l/3Gth of an inch, a mixing containing 61% or total solids and of the following composition Parts by weight Rubber 92.5 Sulphur 2.5 Zinc oxide 2.5 Antioxidant 1.0 Accelerator 0.5 Ammonium oleate 1.0

is prepared according to Patent 1,846,164 and Patent 1,898,604. The alkalinity of the mixing is adjusted by the addition of ammonia so that it is equivalent to 0.25 gm. NHs per 100 gms. The viscosity is then determined in the following manner:-

Place 180 cos. of the mixing in a cylindrical cup 5.2 cms. in diameter which has a tubular orifice 0.318 cm. diameter 1.4 cms long. Note the time taken for the first 50 cos. to flow through the orifice, and add 0.25% ammonia solution to the mixing until this time is 25 seconds at 20 C. The corrected mixing is then caused to flow through orifices into a cold (15 to 20 0.) aqueous dehydrating and setting solution of the following composition:

Gms. per

litre Sodium chloride 200 Ammonium acetate 300 Acetic acid This solution has a pH value of 5.3 measured by means of the quinhydrone electrode.

The thread so formed will be sufiiciently set to withstand subsequent handling after 30 seconds contact with the setting solution.

Example 2 For the production of thread having a diameter of the order or" 1/20th of an inch, a mixing of similar composition to the above is adjusted to an alkalinity equivalent to 0.15 gms. NHs per 100 gm. and to a viscosity which allows 50 cos. to flow from the above mentioned apparatus in 45 seconds. The same procedure is then adopted as in Example 1, but the temperature of the dehydrating and setting solution is braised to 45 C. when the thread will set after 30 second immersion.

Working in accordance with the present invention it is possible to produce thread of a definite count over long periods of time. This constancy of size of thread is equal to, if not better than, that produced by the normal method of making square thread.

What we claim is- 1. A process for the manufacture of threads, filaments and tubes of rubber materials from aqueous dispersions thereof which comprises causing the aqueous dispersions to flow in a shaped jet into contact with a liquid dehydrating and setting medium having a continuous penetrative osmotic action, and comprising a concentrated solution of a largely dissociated hydrolyzable salt of a weak acid and free weak acid itself in such amount that the pH value of the medium is not lower than 5.0, and adding to the aqueous dispersions before contact substances substantially inactive to the dispersions aforesaid and capable of being decomposed when brought into contact with the aforesaid weakly acidic medium into substances inducing coagulation within the aqueous dispersions aforesaid.

2. A process as claimed in claim 1 wherein the substantially inactive substances which are added to the aforesaid dispersions consist of a weak acid and a Weak base.

3. A process as claimed in claim 1 wherein the substantially inactive substances which are added to the aforesaid dispersions are the ammonium soaps of the fatty acids and colophony.

4. A process of forming continuous articles of rubber material from aqueous dispersions thereof which comprises passing said dispersion admixed with a substance substantially inactive thereto and capable of being decomposed by contact with a weakly acidic medium into coagulation inducing substances in a shaped jet into contact with a liquid dehydrating and setting medium having a continuous penetrative osmotic action and comprising a concentrated solution of a largely dissociated salt of a weak acid and free weak acid itself and of a pH value not lower than 5.0.

5. A process of forming articles of rubber ma-V terial from aqueous dispersions thereof which comprises contacting the surface of a shaped mass of said aqueous dispersion admixed with a substance substantially inactive to said dispersion but decomposable by the action of weakly acidic materials into a coagulating material with a liquid dehydrating and setting medium capable of penetrating said aqueous dispersion and containing a concentrated solution of a largely dissociated salt of a free weak acid and the free weak acid itself and of a pH value not lower than 5.0.

6. A method of setting an aqueous dispersion of rubber-like material containing a substance substantially inactive to the dispersion and decomposable by Weakly acidic media into coagulation inducing substances which comprise penetrating said dispersion from the surface thereof with a liquid dehydrating and setting medium comprising a concentrated solution of a largely dissociated salt of a weak acid and the free weak acid itself and of a pH value not lower than 5.0.

EDWARD ARTHUR MURPHY. ROBERT GILBERT JAMES. 

